Method of shaping heated aluminum billets with zinc alloy dies



Filed Sept. 16, 1954 p 29, 95 w. L. WHEE R EIAL 2,906,019

METHOD OF SHAP G HEA ALUMINUM BILLETS WIT INC ALLOY. DIES 3 Sheets-Sheet l INVENTORS WILL L. HEELER LOWELL HALL EVERETT KELLOGG ATTORNEY Sept. 29, 1959 w. WHEEL ETAL 2,906,019

METHOD OF SHAPING HEATE LUMINUM BILLETS WITH ZINC ES ALLOY DI Filed Sept. 16, 1954 3 Sheets-SheetZ INVENTORS L. WHEELER LL E HALL EVERETT J. KELLOGG El IDRNEY Sept. 29, 1959 w. WHEELER :r 2,906,019

. METHOD OF SHAPING HEATED ALUMINUM BILLETS WITH ZINC ALLOY DIES Filed Sept. 16, 1954 3 Sheets-Sheet 3 INVENTORS w||.| L. WHEELER LOWELL E. HALL EVERETT J. KELLOGG BY ATTORNEY United Sttes METHOD OF SHAPING HEATED ALUMINUM BILLETS WITH ZINC ALLOY DIES Application September '16, 1954, Serial No. 456,600

2 Claims. (Cl. 29552.2)

The present invention relates broadly to the art of forging, and is more particularly concerned with a new and improved method of forging.

It has heretofore been the conventional practice when procuring machined parts for the early models of new aircraft to have said parts produced from steel dies. Such forging dies are normally carved from solid steel billets in what is recognized to be a relatively expensive and time-consuming operation. By virtue of the length of time required to fabricate dies from billet stock, and the limited amount of die sinking capacity which is available, it has been frequently necessary to allow an average lead time of at least six months to procure the forging dies.

It is therefore an important aim of the present invention to eliminate the difliculties hereinabove noted, and to provide a method of forging.

Another object of the invention lies in the provision of a material suitable for use in the production of forging dies, and which is characterized by excellent casting properties, ease of polishing and machining, and physical properties approximating those of a mild steel.

Another object of the invention is to provide a forging die material having the foregoing properties, and which is additionally adaptable to welding operations, may be remelted after use, and has good resistance to abrasion.

Still another object of the invention is to provide a forging die material which has improved resistance to intergranular and salt spray corrosion, and whose grain flow, tensile properties, and micro-structure render it particularly suitable for the purposes herein disclosed.

A further object of the invention lies in the provision of a new and improved method of producing a forging die' having the above-noted properties and advantages, and which method is relatively speedy, simple to perform, and productive of accurate and uniform results.

An even further. object of the invention is to provide a method of producing forging dies, including means well adapted to prevent excessive growth of the die cavity and which also provides a convenient procedure for locating the die in a suitable press.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

Figure 1 is an exploded perspective view showing a typical pattern board positioned between a pair of flask members;

Figure 2 is a sectional view of the assembled flasks and pattern board, and showing a method of forming a plaster face pattern;

Figure 3 is a sectional view of the assembled flasks with the pattern board removed, and showing the formation of a sand mold from a plaster face pattern;

Figure 4 is a fragmentary sectional view of the assembled flask members, and illustrating the casting of the herein disclosed die from a sand mold;

atent O 2,906,019 Patented Sept. 29, 1959 2 Figure 5 is a perspective view of a pattern board carrying thereon the shape to be produced; I Figure 6 is a perspective View of a suitable retainer member; a 7

Figure 7 is a sectional view of a pattern board and retainer member in assembled relation, and showing a I method of forming a plaster pattern combination;

Figure 8 is a perspective view of the plaster pattern combination;

Figure 9 is a sectional view of a suitable foundry flask arranged insurrounding relation to a plaster pattern combination and showing one manner of forming a sand mold therefrom; k

Figure 10 is a perspective view of a sand mold formed in the manner shown in Figure 8'; and

Figure 11 is an exploded perspective view of a method of retaining the dies in substantially rigid relation during the production of parts therefrom.

While any one-of'a number of different forging methods may be found suitable in the production of a forging die having the foregoing characteristics and advantages, one method which has proven itselfwell' adapted forthis purpose is illustrated in Figures I through 4, and reference is now made thereto. I

As is shown in Figure 1', there is preferably provided an upper flask 20 and a lower flask 21, between which may be located a pattern board 21 carrying upon its face the shape 23' to be produced in the final die. Each of the fl'asks 20 and 21 are in the shape of open-ended, substantially rectangular shell-like members formed of metal and provided with inner walls 24 tapered to permit the ready removal of the casting. materials therefrom. In accordance with current practice,- the pattern board 22 is preferably constructed of Wood as is the part shape 23 carried upon one surface of said board.

An initial step in the provision of thepresent die is the formation of a plaster face pattern having a cavity of the shape desired. This may be accomplished by first arranging the flasks 2'0 and 21 and pattern board 22 in assembled relation as shown in Figure 2, and placing a predetermined amount of plaster 25 in the upperflask 20 in=close conformity withthe contours-of the shape 23. To securely maintain the plaster- 25 within theflask 20 and to provide a substantially even foundation for each of said flasks. 20 and 21, a board-like member 26- may be located over. the openendof each ofthe flasks 20'and 21*.

Subsequentto the setting-of the plaster 25 andremoval of the pattern board 22, the pair of flasks:20 and 21 are turned over to place the empty flask 21 in an uppermost position with respect to the flask 20. A suitable quantity of foundry sand 27 is then placed in the flask 21 and securely tamped' therein to assure a substantially complete filling of the cavity in the plaster face pattern 28. After a proper male sand impression has been made from the plaster face pattern 28, the relative position of the flasks 20 and' 21 is reversed and the plaster face" pattern 28 removed from within the flask 20.

To obtain the final die from the sand mold 29 carried by the flask 21, a predetermined molten quantity of one of the forging die materials herein disclosed is poured into the upper flask 2'0 and a metallic die 30 formed therein.

As an alternative procedure in the production of the subject forging die, the method illustrated in Figures .5 and 10 may be employed. In accordance with this technique, a pattern board 31 of the character shown in Fig. 5 may be used and a raised pattern of the shape 32 to be formed mounted thereon. A shell-like retainer member 33, which is preferably constructed of aluminum and is provided with angularly disposed side and end walls 34 and 35,, is then located upon said pattern board 31 in surrounding relation to the pattern shape 32. As may be seen in Fig. 6, said retainer member is constructed with beveled corners 36 to facilitate removal of the forg ing and pattern making materials.

A mounting board 38, having an opening 39 provided centrally thereof, is next secured to the end and side walls 34 and 35 of the retainer 33, as by screws or the like 40 passing into the ends of said walls. Upon propor setting of the plaster 37, the structure shown in Fig. 7 is turned over and the mounted pattern board 31 removed therefrom, to provide a plaster pattern combination 41 of the character shown in Fig. 8. A foundry fiask 42 may then be properly located upon the plaster pattern combination and sand 43 compactly arranged in surrounding relation to said combination in the manner of Fig. 9. Subsequent to this step, the flask 42 is rotated 180 from the position shown in Fig. 9, the plaster pattern combination 41 removed therefrom, and a made up sand mold 44 of the character indicated in Fig. thereby produced. The cavity 45 in said sand mold may thereupon be filled with a forging die material of the type herein disclosed to produce the final forging die.

With particular reference now to the forging die material itself, it has been found that a zinc base alloy, identified by its manufacturer, National Lead Company, as Kirksite A alloy, is productive of the most satisfactory results. While certain metallic substances such as meehenite, cast ductile iron, and some of the cast steels have properties which render them in certain ways suitable for forging die use, the material Kirksite has several advantages thereover. And among those characteristics which favor the use of this particular zinc base alloy are its relatively high resistance to abrasion, the ease with which it may be polished and machined, its similarity to mild steel insofar as physical properties are concerned, and the fact that special foundry equipment is generally not needed to work it properly.

While it is to be understood that variations in the composition of the Kirksite die material are possible to render it more suitale for different forging uses, it has been found that the following composition is effective to accomplish the objectives herein stated:

Percent by weight A compound of the above character has been found to have an ultimate tensile strength of 37,860 lbs/sq. in, 3.0% elongation in 2 inches, an ultimate compressive strength of 77,800 lbs./ sq. in., a shear strength of 34,000 lbs/sq. in., and a weight of 0.25 lb./cubic inch. It may thus be seen that it is Well adaptedto the production of forging dies for use with aluminum alloy materials.

The foregoing composition has a melting point of approximately 745 F., and while in a molten condition within the temperature range of 775 to 900 F., may be poured into the upper flask 20 shown in Fig. 4 or into the sand mold of Fig. 10 to form the desired forging die. Subsequent to processing the Kirksite die through a'suit able finishing operation, as by planing said die to remove any rough edges and to obtain a substantially flat bottom thereon, the die may be employed in the manner shown in Fig. 11 to produce parts therefrom.

As may be seen in the noted exploded perspective view, there is herein provided a ram plate 46 formed on its upper surface with a wedgelike section 47 for engagement with complementary means on a conventional press. Provided also are a pair of upper and lower die inserts 48 and 49, said means constituting the dies formed in the manner earlier described. Positioned for operative engagement with said lower die insert 49 is a bottom ram plate 50 having therein tapped holes 51 for the reception of screws or other means adapted to pass through aligned tapped holes 52 in the upper ram plate 46.

To assure that there will be no excessive growth of the cavities in the die inserts 48 and 49, and further to provide what has been found to be a convenient method of locating said inserts in a suitable press, there is also herein provided a pair of die retainer members 53 and 54. As appears in Fig. 11, each of said retainer members comprises an open-faced base plate 55 to which is secured by bolts or the like 56 a die receiving frame 57. Each of said frames are provided with inwardly tapering inner side and end walls 58 and 59, as well as tapered beveled corners 60. By means of this arrangement there is not only provided a close fitting contact between the die inserts 48 and 49 and their respective retainer membars 53 and 54, but also a construction whereby the die inserts may be readily removed from the retainers upon completion of the forging operation.

In the production of forged parts, a piece of heated billet stock, as for example an aluminum alloy such as 148 alloy, is preferably first located in the blocker die cavity 61 of the lower die insert 50, and the ram plates 46 and 50 fixedly secured to one another by fastening means passing through loaded die retainers 53 and 54. The assembly thus formed is then subjected to a forging opera tion of the character which may be provided by the instantaneous action of a mechanical press, or the repetitive action of forging hammers. Thereafter, in the course of a regular production run, the part formed in the blocker die cavity 61 may be transferred to the finish die cavity 62, the blocker cavity again loaded with heated billet stock, and the pressing or forging operation repeated.

It has been found that the most satisfactory results are obtained by raising the temperature of the aluminum stock to approximately 600-900 F, and more spmifically, in the range of 800-820 F., and by maintaining the temperature of the die inserts themselves at a point not substantially in excess of 300 F. Inasmuch as the Kirksite alloy earlier described has a melting point in the neighborhood of 745 F., it is of course important that the temperature of the die not approach this particular temperature. As a matter of fact, knowing the closeness of melting temperatures between Kirksite and conventional aluminum alloys, applicants were quite surprised to find this zinc base alloy suitable for forging operations. Aluminum is by practice often forged at around 850 F., and during repeated cycles of producing parts, it was anticipated that a die formed of Kirksite would soon absorb sufficient heat from the stock to break down the Kirksite material. However, considerable work along these lines has shown that a material of a relatively high melting point such as Kirksite can be effectively used even at conventional forging operation temperatures by carefully controlling such conditions as the duration of time within which the part is in the die. To accomplish this, it is desirable that the forged part be removed from the die substantially immediately after setting, and before the die reaches a temperature of about 300-350 F. Extensive testing has been done .of parts produced from Kirksite dies in the manner above described. As for example, 14S-T6 aluminum alloy forgings were etched in a 10% solution of sodium hydroxide and showed no apparent seams, laps, or other surface defects. Further forgings of this same material were also cross sectioned parallel to the flash and parallel to the ends after which they were etched in a 10% solution of sodium hydroxide Photographs made of these cross sections showed favorable grain flow and a marked absence of defects. In addition, accelerated corrosion tests were conducted on various sections of the 14ST6 aluminum alloy forgings and no extensive attack was noted on any surface. .And even further, a hour salt spray test, followed by a microscopic examination, revealed no evidence. of intergranular corrosion.

Forgings produced by the herein disclosed procedure were examined as to their physical properties. Several locations were taken after heat treatment and it was found that the specimens had a yield strength in the range of 59,000 to 60,750 lbs/sq. in.; a tensile strength within the range of 67,100 to 68,400 lbs/sq. in.; and an elongation of 4.2 to 13.3 percent in two inches.

It may thus be seen that the novel process and article herein disclosed fills a need which has long existed in the art. Not only may the normal lead time of approximately six months required in procurement of heretofore used forging dies be substantially reduced, but the cost of the dies themselves is greatly reduced with no noticeable sacrifice in accuracy. Further, by utilizing the present method, forgings may be employed having physical properties superior to parts carved from billet stock.

And in addition, the forging die material herein disclosed may be readily melted down to thereby permit the reuse of material obtained from dies which have been rendered obsolete by design changes.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred embodiment of the same, but that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims.

We claim:

1. A method of shaping a workpiece from a billet of aluminum or the like, comprising the steps of locating a heated billet of aluminum and its alloys that is heated to a temperature within the range of from approximately 800 F. to approximately 850 F. upon a cavity provided in a cast hot forge die fabricated from a zinc base alloy which includes not less than about by weight of zinc and not more than a total of about 15% by weight of copper, aluminum and lead and having a melting point temperature of approximately 750 F., applying comparatively short-time pressure to said heated billet to thereby force said billet into intimate contact with the die cavity to shape a workpiece therein, and removing the shaped workpiece from the cavity prior to the surfaces of said cavity reaching a temperature approximately 350 F. 1

2. A method of shaping as defined in claim 1, in which the zinc alloy includes from approximately 2.5% to approximately 3.5% by weight of copper, from approximately 3.5% to approximately 4.5% by weight of aluminum, approximately 1.0% by weight of lead, and approximately 90.0% by weight of zinc.

References Cited in the file of this patent UNITED STATES PATENTS 1,314,611 Stafford Sept. 2, 1919 1,401,577 Becker Dec. 27, 1921 1,621,573 Armour Mar. 22, 1927 1,675,264 Fuller June 26, 1928 1,852,441 Anderson Apr. 5, 1932 1,889,823 Cole Dec. 6, 1932 2,070,474 Dacco Feb. 9, 1937 2,306,861 Broughton Dec. 29, 1940 2,358,667 Stern Sept. 19, 1944 2,494,935 Dunn Jan. 17, 1950 2,512,484 Cornell June 20, 1950 

1. A METHOD OF SHAPING A WORKPIECE FROM A BILLET OF ALUMINUM OR THE LIKE, COMPRISING THE STEPS OF LOCATING A HEATED BILLET OF ALUMINUM AND ITS ALLOYS THAT IS HEATED TO A TEMPERATURE WITHIN THE RANGE OF FROM APPROXIMATELY 800*F. TO APPROXIMATELY 850*F. UPON A CAVITY PROVIDED IN A CAST HOT FORGE DIE FABRICATED FROM A ZINC BASE ALLOY WHICH INCLUDES NOT LESS THAN ABOUT 85% BY WEIGHT OF ZINC AND NOT MORE THAN A TOTAL OF ABOUT 15% BY WEIGHT OF COPPER, ALUMINUM AND LEAD AND HAVING A MELTING POINT TEMPERATURE OF APPROXIMATELY 750*F., APPLYING COMPARATIVELY SHORT-TIME PRESSURE TO SAID HEATED BILLET TO THEREBY FORCE SAID BILLET INTO INTIMATE CONTACT WITH THE DIE CAVITY TO SHAPE A WORKPIECE THEREIN, AND REMOVING THE SHAPED WORKPIECE FROM THE CAVITY PRIOR TO THE SURFACES OF SAID CAVITY REACHING A TEMPERATURE APPROXIMATELY 350*F. 